1. Field of the Invention
This invention relates generally to a high-pressure, controlled-expansion hose suitable for power steering applications, more particularly to an expansion hose with a textile reinforcement layer comprising both nylon and polyester filaments, and specifically to an expansion hose with a first braided reinforcement layer of nylon and a second braided reinforcement layer of polyester.
2. Description of the Prior Art
Expansion hoses are used in high pressure fluid transfer systems or fluid power systems, such as hydraulic systems, power steering systems, or the like. In such dynamic applications, where a hose is subject to pressure pulsation, an expansion hose with a controlled or predetermined amount of volumetric expansion may be useful for smoothing pressure fluctuations, damping vibrations, reducing noise, or otherwise improving the response of the system to pressure pulses. Volume expansion refers to the variation of inner volume of hose when supplied with a high pressure fluid. Controlled expansion refers to a hose designed to exhibit a predetermined amount of volumetric expansion at a given internal pressure. Such a hose is commonly referred to as “expansion hose.” One classification scheme which may be used for expansion hose is based on the volumetric expansion per unit length of hose, specified in cc/m. For example, a standard issued by SAE International, SAE J2050, describes expansion hose for power steering pressure hose applications as having volumetric expansion in the range from 10 to 46 cc/m at 9.0 MPa internal pressure for a hose having an internal diameter (“ID”) of 9.85 mm. Another specification, issued by a vehicle manufacturer calls for high expansion power steering hose to exhibit from 27 to 40 cc/m volumetric expansion at 9.0 MPa for an ID of about 10 mm. Thus, expansion hose may somewhat arbitrarily be further classified as low expansion hose or high expansion hose. Low expansion hose may have a relative volumetric expansion of about 13% to about 35% at a predetermined maximum working pressure. High expansion hose may have a volumetric expansion of more than about 35% at a predetermined maximum working pressure.
The expansion hose is generally designed to have a burst pressure of about four times the maximum working pressure. High burst pressure may generally be obtained by using reinforcing layers of high strength wires, fibers, or yarns. But high burst pressure and high volumetric expansion may be opposing goals.
Fatigue resistance is also required when expansion hoses are subjected to dynamic conditions, such as repeated high pressure pulses. For example, SAE J2050 calls for minimum performance of 200,000 pressure cycles that peak at 100% of the design working pressure of 10.5 MPa. Unfortunately, as demands on expansion hose move generally toward higher pressures, temperatures and fatigue resistance, the three goals of having a certain minimum burst pressure, a predetermined volumetric expansion at a certain working pressure, and a high impulse fatigue resistance are found to be in opposition. Simply increasing the working pressure will increase the volumetric expansion and decrease the fatigue life. Increasing the amount of reinforcement can increase the burst pressure, but at the same time will decrease the volumetric expansion. Reinforcement parameters, such as braid angle or spiral angle, can be used to control volumetric expansion somewhat, but deviations from the usual optimum settings also cause negative effects on other aspects of hose performance such as length stability.
U.S. Pat. No. 5,172,729 discloses an example of an expansion hose having an inner flexible hollow body which extends coaxially to an outer pressure hose. Such dual hose designs are complex.
U.S. Pat. No. 7,063,181 discloses a power steering hose having a multi-layer inner core, covered with two tubular reinforcement layers in the form of a braid or spiral or woven material such as nylon. The expansion of the hose is reported to be controlled through the elongation of the yarn and the angle at which it is applied, but no examples thereof are offered.
U.S. Pat. No. 5,660,210 discloses a reinforced hose having at least two reinforcing thread layers, including a lower layer of a polyester thread having 10% elongation at break, and an upper layer of polyester or polyvinyl alcohol thread. The resulting hose is reported to have excellent fatigue resistance but very small volume expansion. U.S. Pat. No. 5,660,210 teaches that there has been no reinforcing thread which satisfies both characteristics, i.e. fatigue resistance and volume expansion, simultaneously. Even when the materials of the two layers are varied, no construction has yet satisfactorily reconciled these two contradictory characteristics.
U.S. Pat. No. 6,807,988 discloses a thermoplastic reinforced hose construction having at least a first and a second reinforcing layer of a first and a second fiber, with the two layers bonded together by a bonding agent that is controlled to wet only a portion of the filaments. Radial expansion and axial elongation are said to be affected by the pitch angle of spiraled layers, which are oppositely wound in pairs to counterbalance torsional twisting effects.
U.S. Pat. No. 5,316,046 discloses a power steering hose having one or more reinforcement layers of organic fibers. The hose exhibits a volumetric expansion of 20 to 26 cc/m at 9 MPa (6-8 cc/ft at 91 kgf/cm2), which corresponds to about 35% volumetric expansion.
U.S. Pat. No. 5,077,108 discloses composite laminates for hose including fibrous reinforcements in the form of braids of a material selected from nylons, polyesters, rayons, cottons, vinylons, aramids, and the like.
U.S. Pat. No. 6,677,018 discloses a high pressure hose having a plurality of reinforced layers including a steel wire reinforced layer and an organic fiber reinforced layer based on aromatic polyamide.
U.S. Pat. No. 7,143,789 discloses a high pressure hose having an odd number of layers of reinforcing plies which are preferably identical or at least their moduli of elasticity are similar.
U.S. Pat. No. 3,383,258 discloses a high pressure hose having at least one layer of braided yarn comprising polyester filaments.
U.S. Pat. No. 3,605,818 discloses a high pressure hose having at least one braided layer of a binder-impregnated ribbon of untwisted multi-filament yarns comprising synthetic or natural filaments. A preferred material is a biconstituent filament of melt-blended nylon and polyester.
Japanese Unexamined Patent Publication JP 02-147328 discloses a cord for reinforcing resin hose comprising a core-sheath composite fiber of polyester core and nylon sheath. However, it is known in the art that blends of two fibers of different properties generally do not follow a linear relationship with blend proportion, and the resultant property is generally less than proportional. (See e.g. Wellington Sears Handbook of Industrial Textiles, §292 (1963).)
U.S. Pat. No. 4,898,212 discloses a flexible reinforced hose having a pair of oppositely helically wound layers of reinforcement comprising a first fiber (aromatic polyamide) having a tenacity of about 12 to about 25 grams for denier and an elongation at break of about 2% to about 8% that are disposed in alternating contiguous relationship to a second fiber (preferably polyester) having a tenacity of from about 7 to 11 grams per denier and an elongation at break of about 9% to about 17%. An example hose having a first braided layer of Kevlar and a second braided layer of polyester exhibited inferior flex fatigue resistance. The volumetric expansion of the disclosed hoses was too low to be considered expansion hose.